"Ken Scharf" wrote in message
. ..
Reg Edwards wrote:
Bipolar and MOSFET amplifiers are by comparison low impedance

devices

==============================
Actually they are not. But everything else you say is quite
correct.


Well their INPUT IMPEDANCE can be high, but their
OUTPUT IMPEDANCE when used as a power amp is just as
low as bipolar transistors, so the broadband transformers
are just as valid. And as far as their input impedance,
well these are class AB or B power amps, so they take
some driving power. In this case because of the required
driving power, the input impedance isn't very high.
=======================================

This little discussion is about the relative internal resistance of
tubes and transistors. It has nothing to do with driving resistance
which, in the case of tubes and FET transistors, are both very high.

Somebody said the internal resistance of transistors, in general, was
much lower than that of tubes. He was incorrect.

Of course, it is possible to find an example of a high power
transistor which has a lower internal resistance than a given low
power tube.

But, in general, transistors have high internal resistances, greater
than tubes.

To base conclusions on the greatly different working voltages and
currents of devices is entirely incorrect. But it is easily done and
leads to misunderstandings when novices and learners attempt to
analyse circuit operation.
----
Reg, G4FGQ